Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A solar-powered supercritical carbon dioxide turbine system includes a
supercritical carbon dioxide turbine system and a solar heating system.
The solar heating system has a molten salt heat transfer fluid for
providing thermal energy to the supercritical carbon dioxide turbine
system.

Claims:

1. A turbine system comprising:a supercritical carbon dioxide turbine
having an outlet;a high temperature recuperator having a first inlet
connected to the outlet of the supercritical carbon dioxide turbine and a
first outlet;a low temperature recuperator having a first inlet connected
to the first outlet of the high temperature recuperator and a first
outlet;a first valve having an inlet, a first outlet and a second outlet,
wherein the first inlet of the first valve is connected to the first
outlet of the low temperature recuperator;a compressor connected to the
first outlet of the first valve;a precooler connected to the second
outlet of the first valve; anda solar heating system having a molten salt
heat transfer fluid for providing thermal energy to the supercritical
carbon dioxide turbine.

2. The turbine system of claim 1, wherein the supercritical carbon dioxide
turbine operates at a temperature of at least about 1022 degrees
Fahrenheit.

3. The turbine system of claim 1, wherein the molten salt heat transfer
fluid comprises between about 50% sodium nitrate and about 70% sodium
nitrate and between about 30% potassium nitrate and about 50% potassium
nitrate by weight.

4. The turbine system of claim 1, wherein the solar heating system heats
the molten salt heat transfer fluid to a temperature of at least about
1065 degrees Fahrenheit.

6. The turbine system of claim 1, and further comprising a heat exchanger,
wherein the thermal energy is transferred from the molten salt heat
transfer fluid to a carbon dioxide Brayton cycle working fluid.

7. A system for providing energy for a supercritical carbon dioxide
turbine, the system comprising:a Brayton cycle working fluid for
providing energy to the supercritical carbon dioxide turbine;a high
temperature recuperator that receives the Brayton working fluid from the
supercritical carbon dioxide turbine and cools it;a low temperature
recuperator that receives the Brayton working fluid from the high
temperature recuperator and cools it;a precooler;a first valve that
divides the Brayton cycle working fluid cooled by the low temperature
recuperator into a first portion that flows through the precooler and a
second portion that does not flow through the precooler;a second valve
that combines the first portion of the Brayton cycle working fluid that
is cooled by the precooler and the second portion of the Brayton cycle
working fluid that is not cooled by the precooler; anda solar receiver
for heating a heat transfer fluid to a temperature of at least about 1065
degrees Fahrenheit, wherein the heat transfer fluid is in communication
with the Brayton cycle working fluid.

8. The system of claim 7, wherein the supercritical carbon dioxide turbine
operates at an inlet temperature of about 1022 degrees Fahrenheit.

10. The system of claim 9, wherein the molten salt heat transfer fluid
comprises between about 50% sodium nitrate and about 70% sodium nitrate
and between about 30% potassium nitrate and about 50% potassium nitrate
by weight.

11. The system of claim 9, wherein the heat transfer fluid provides
thermal energy to the supercritical carbon dioxide turbine.

12. The system of claim 11, and further comprising a heat exchanger,
wherein the thermal energy is transferred from the molten salt to carbon
dioxide.

13. The system of claim 7, wherein the system is a solar heating system.

14. A method of generating electricity with a supercritical carbon dioxide
turbine, the method comprising:capturing solar energy from
sunlight;heating a heat transfer fluid to a temperature of at least about
1065 degrees Fahrenheit with the solar energy;transporting energy from
the heat transfer fluid to heat a Brayton cycle working fluid of the
supercritical carbon dioxide turbine;passing the heated Brayton cycle
working fluid through the supercritical carbon dioxide turbine;cooling
the Brayton cycle working fluid from the supercritical carbon dioxide
turbine with a high temperature recuperator;cooling the Brayton cycle
working fluid from the high temperature recuperator with a low
temperature recuperator;dividing the cooled Brayton cycle working fluid
from the low temperature recuperator into a first portion and a second
portion;cooling the first portion of the Brayton cycle working fluid;not
cooling the second portion of the Brayton cycle working fluid;
andcombining the first portion of the Brayton cycle working fluid and the
second portion of the Brayton cycle working fluid that is not cooled
after the step of cooling the first portion of the Brayton cycle working
fluid.

17. The method of claim 16, wherein the molten salt heat transfer fluid
comprises between about 50% sodium nitrate and about 70% sodium nitrate
and between about 30% potassium nitrate and about 50% potassium nitrate
by weight.

18. The method of claim 14, wherein transporting the energy of the heat
transfer fluid to heat the Brayton cycle working fluid of the
supercritical carbon dioxide turbine comprises using a heat exchanger.

[0002]There is a continuing demand for clean renewable energy sources due
to the depletion of the Earth's supply of fossil fuels and concerns over
the contribution to global warming from combustion of fossil fuels. Solar
power towers generate electric power from sunlight by focusing
concentrated solar radiation on a tower-mounted receiver. Solar power
tower systems typically include a "cold" storage tank, a solar receiver,
heliostats, a "hot" storage tank, and an energy conversion system, such
as a steam generator and turbine/generator set. In operation, a heat
transfer fluid is pumped from the cold storage tank to the solar
receiver. The heat transfer fluid can be any appropriate medium that has
the capability to transfer heat and thermally maintain the heat in the
medium, such as water, liquid metal, or molten salt.

[0003]The solar receiver is typically positioned 50 feet to 250 feet or
more above ground and is heated by the heliostats. The heliostats
redirect and concentrate solar radiation from the sun onto the solar
receiver. The heat transfer fluid flows through receiver tubes of the
solar receiver where it is heated by the concentrated solar energy. In
the solar receiver, liquid metals have been used as the heat transfer
fluid and can reach temperatures of approximately 1600 degrees Fahrenheit
(° F.). Water/steam being used as the heat transfer fluid can
reach peak temperatures of approximately 1050° F. Molten salts
currently being used as the heat transfer fluid can reach temperatures of
approximately 1100° F.

[0004]After the heat transfer fluid has been heated in the solar receiver,
the heat transfer fluid typically flows into the hot thermal storage
tank. The heat transfer fluid is then stored in the hot thermal storage
tank until it is needed for electrical power generation. The hot thermal
storage tank allows for electrical power production during cloudiness or
darkness. When electrical energy is needed, the hot heat transfer fluid
is pumped from the hot storage tank to an energy conversion system. The
heat transfer fluid transfers the heat within the energy conversion
system. The energy conversion system can be, for example, a Rankine cycle
conversion system or a Brayton cycle conversion system. Brayton cycles,
with the use of a regenerator (also called a recuperator) typically have
higher efficiencies than Rankine cycles, which have efficiencies of
approximately 34% to 40%. After the heat has been removed from the heat
transfer fluid, the heat transfer fluid is transported back to the cold
storage tank for reuse.

[0005]Due to the concern of depleting natural resources and the effect of
pollution on global warming, there is a need in the art for a method of
producing electricity using renewable resources. In addition, solar power
facilities typically have high capital costs, thus, there is also a need
in the art for a method of producing electricity in an efficient and
cost-effective manner.

BRIEF SUMMARY OF THE INVENTION

[0006]A turbine system includes a supercritical carbon dioxide turbine and
a solar heating system. The solar heating system has a molten salt heat
transfer fluid for providing thermal energy to the supercritical carbon
dioxide turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a schematic of a turbine system.

[0008]FIG. 2 is a diagram of a method of using molten salt as the heat
transfer fluid of a solar heating system.

DETAILED DESCRIPTION

[0009]FIG. 1 shows a schematic of turbine system 10, which generally
includes solar heating system 12 and supercritical carbon dioxide turbine
system 14. Solar heating system 12 is used to provide thermal energy to
supercritical carbon dioxide turbine system 14 up to 24 hours a day. The
use of solar heating system 12 in conjunction with supercritical carbon
dioxide turbine system 14 allows for efficient use of supercritical
carbon dioxide turbine system 14 and increases the electric conversion
efficiency of supercritical carbon dioxide turbine system 14 to
approximately 46%. This increases the overall efficiency of turbine
system 10, reducing plant capital costs and electricity production costs.

[0011]In operation, the heat transfer fluid is stored in cold storage tank
18. The heat transfer fluid is pumped through cold pump 32a to solar
receiver 20. Heliostats 22 redirect and concentrate solar radiation from
the sun onto solar receiver 20, which converts the redirected sunlight to
thermal energy. The heat transfer fluid flows through solar receiver 20
where it is heated by the concentrated solar energy. Solar receiver 20 is
capable of withstanding temperatures of at least approximately 1065
degrees Fahrenheit (° F.). In one embodiment, solar heating system
12 is a solar power tower system.

[0012]After the heat transfer fluid has been heated in solar receiver 20
to the desired temperature, the heat transfer fluid flows into hot
thermal storage tank 24. The heat transfer fluid is then stored in hot
thermal storage tank 24 until it is needed by supercritical carbon
dioxide system 14 to produce electricity. Hot thermal storage tank 24
allows for power production during cloudiness or darkness.

[0013]When electricity generation is needed, the heated heat transfer
fluid is pumped from hot thermal storage tank 24 and circulated through
heat exchanger 26 to provide thermal energy to supercritical carbon
dioxide system 14. After the heat transfer fluid has passed through heat
exchanger 26, the extracted thermal energy from the heat transfer fluid
results in a drastic drop in the temperature of the heat transfer fluid
to approximately 800° F. The heat transfer fluid is then sent back
to cold storage tank 18, where it is stored in closed cycle solar heating
system 12 for reuse.

[0014]The heat transfer fluid can be any fluid that has the capability to
transfer heat and thermally maintain the heat in the fluid, such as
water, liquid metal, or molten salt. The heat transfer fluid may also
interact with a solid heat transfer media contained in cold and hot
storage tanks 18 and 24. In an exemplary embodiment, molten salt is used
as the heat transfer fluid through solar heating system 12. The molten
salt used to transfer heat from solar receiver 20 to supercritical carbon
dioxide system 14 is capable of being heated to a temperature of at least
approximately 1065° F. The molten salt can be salts composed of a
eutectic mixture of sodium nitrate and potassium nitrate. A suitable
composition of the molten salt is between approximately 50% and
approximately 70% sodium nitrate by weight and approximately 30% and
approximately 50% potassium nitrate by weight. A more suitable
composition of the molten salt is approximately 60% sodium nitrate by
weight and approximately 40% potassium nitrate by weight.

[0015]Supercritical carbon dioxide turbine system 14 generally includes
circulation system 34, heat exchanger 26, turbine 36, turbine generator
38, high temperature recuperator 40, low temperature recuperator 42,
precooler 44, main compressor 46, and recompression compressor 48.
Circulation system 34 transports a Brayton cycle working fluid through
supercritical carbon dioxide system 14 and generally includes high
temperature line 50, first intermediate temperature line 52, high
temperature recuperator outlet line 54, second intermediate temperature
line 56, low temperature recuperator outlet line 58, third intermediate
temperature line 60, precooler line 62, main compressor line 64, low
temperature recuperator inlet line 66, recompression compressor inlet
line 68, recompression compressor outlet line 70, first valve 72, second
valve 74, and high temperature recuperator inlet line 76. The Brayton
cycle working fluid is circulated through circulation system 34 by main
compressor 46 and recompression compressor 48. In addition, generator 38,
turbine 36, recompression compressor 48, and main compressor 46 are
connected on shaft 78. Main compressor 46 and recompression compressor 48
are connected to each other through first shaft section 78a.
Recompression compressor 48 and turbine 36 are connected to each other
through second shaft section 78b. Turbine 36 and generator 38 are
connected to each other by third shaft section 78c. In an exemplary
embodiment, supercritical carbon dioxide system 14 is a supercritical
carbon dioxide Brayton power conversion cycle.

[0016]As the heat transfer fluid from solar heating system 12 passes
through heat exchanger 26, the heat is transferred to the Brayton cycle
working fluid flowing through supercritical carbon dioxide system 14. In
an exemplary embodiment, supercritical carbon dioxide is used as the
Brayton cycle working fluid flowing through supercritical carbon dioxide
system 14. The supercritical carbon dioxide flowing through supercritical
carbon dioxide system 14 has the capability of being heated to a
temperature of approximately 1022° F. As the thermal energy is
exchanged from the molten salt of solar heating system 12 to the
supercritical carbon dioxide of supercritical carbon dioxide system 14 in
heat exchanger 26, the supercritical carbon dioxide is heated to a
temperature of approximately 1022° F. and a pressure of
approximately 2876 pounds per square inch (psi) as it leaves heat
exchanger 26 and flows through high temperature line 50. High temperature
line 50 transports the supercritical carbon dioxide from heat exchanger
26 to turbine 36.

[0017]At turbine 36, the Brayton cycle working fluid is allowed to expand
and release energy, reducing the temperature of the Brayton cycle working
fluid to approximately 825° F. and approximately 1146 psi. The
energy released during the expansion process in turbine 36 is sufficient
to turn main compressor 46, recompression compressor 48, and generator 38
on shaft 78. Generator 38 uses the mechanical energy from turbine 36 to
turn a generator which generates electricity. In an exemplary embodiment,
generator 38 generates approximately 300 MegaWatts of electrical energy
net, with an efficiency of approximately 90%. The power generated by
generator 38 may be used in various applications, including, but not
limited to: powering commercial and residential buildings.

[0018]The Brayton cycle working fluid is then transported from turbine 36
to high temperature recuperator 40 through first intermediate temperature
line 52. In high temperature recuperator 40, the temperature of the
Brayton cycle working fluid drops to approximately 335° F. The
Brayton cycle working fluid is then passed through second intermediate
temperature line 56 to low temperature recuperator 42, where the
temperature of the Brayton cycle working fluid is further reduced to
approximately 158° F. High temperature and low temperature
recuperators 40 and 42 function as heat exchangers that recapture heat
and send the heat back into supercritical carbon dioxide system 14 to
improve the efficiency of supercritical carbon dioxide system 14. Thus,
heat is added to the Brayton cycle working fluid in high and low
temperature recuperators 40 and 42, as well as in heat exchanger 26.

[0019]From low temperature recuperator 42, the Brayton cycle working fluid
is sent through third intermediate temperature line 60 to first valve 72.
At first valve 72, a portion of the Brayton cycle working fluid is passed
through precooler line 62 to precooler 44 where the temperature of the
Brayton cycle working fluid is reduced to approximately 90° F.
before the Brayton cycle working fluid is transported through main
compressor line 64 to main compressor 46. Precooler 44 may reject the
heat into water, which is sent to a cooling tower to release the heat to
the atmosphere. Alternatively, the heat rejection may also be
accomplished by directly air cooling the heat. The cooling is required to
lower the temperature of the Brayton cycle working fluid to the required
low starting temperature of closed supercritical carbon dioxide system
14. At main compressor 46, the Brayton cycle working fluid is pressurized
to a pressure of approximately 2900 psi and a temperature of
approximately 142° F. By operating main compressor 46 with inlet
conditions immediately above the carbon dioxide critical point, the work
required is significantly reduced. The Brayton cycle working fluid then
flows through low temperature recuperator inlet line 66 back to low
temperature recuperator 42 and is heated to a temperature of
approximately 317° F. The Brayton cycle working fluid then leaves
low temperature recuperator 42 and enters second valve 74 through low
temperature recuperator outlet line 58.

[0020]In parallel, the second portion of the Brayton cycle working fluid
is transported from first valve 72 through recompression compressor inlet
line 68 to recompression compressor 48 where it is pressurized to
approximately 2899 psi at a temperature of approximately 317° F.
The Brayton cycle working fluid from recompression compressor 48
subsequently rejoins the main compressor 46 discharge through
recompression compressor outlet line 70 into second valve 74. The
combined Brayton cycle working fluid then leaves second valve 74 through
high temperature recuperator inlet 76 and enters high temperature
recuperator 40, where it is heated to approximately 746° F. From
high temperature recuperator 40, the Brayton cycle working fluid is
passed through high temperature recuperator outlet line 54 and enters
heat exchanger 26 at a temperature of approximately 746° F. and a
pressure of approximately 2895 psi.

[0021]FIG. 2 shows a diagram of a method of using the heat transfer fluid
from solar heating system 12 to provide thermal energy to supercritical
carbon dioxide system 14. As previously mentioned, the molten salt is
initially stored in cold storage tank 18, Box 100. When needed, the
molten salt is pumped to solar receiver 20 (Box 102) and heated to a
temperature of at least approximately 1065° F., Box 104. As shown
in Box 106, the heated molten salt is then sent to hot storage tank 24
until it is needed by supercritical carbon dioxide system 14. The heated
molten salt is pumped to supercritical carbon dioxide system 14, where
the thermal energy from the molten salt is transferred to the
supercritical carbon dioxide to power supercritical carbon dioxide system
14, Box 108.

[0022]The turbine system uses a molten salt solar heating system to
provide thermal energy to a supercritical carbon dioxide system. The
supercritical carbon dioxide system requires peak carbon dioxide
temperatures of approximately 1022° F. The solar heating system
passes molten salt as a heat transfer fluid through the solar heating
system to transport the thermal energy required to power to supercritical
carbon dioxide system. In an exemplary embodiment, the solar heating
system is a solar power tower system that heats the molten salt to a
temperature of approximately 1065° F.

[0023]Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize that
changes may be made in form and detail without departing from the spirit
and scope of the invention.